title: Let-7b expression determines response to chemotherapy through the regulation of cyclin D1 in glioblastoma.
abstract: BACKGROUND
  Glioblastoma is the most common type of primary brain tumors. Cisplatin is a commonly used chemotherapeutic agent for Glioblastoma patients. Despite a consistent rate of initial responses, cisplatin treatment often develops chemoresistance, leading to therapeutic failure. Cellular resistance to cisplatin is of great concern and understanding the molecular mechanisms is an utter need.
  
  
  METHODS
  Glioblastoma cell line U251 cells were exposed to increasing doses of cisplatin for 6 months to establish cisplatin-resistant cell line U251R. The differential miRNA expression profiles in U251 and U251R cell lines were identified by microarray analysis and confirmed by Q-PCR. MiRNA mimics were transfected into U251R cells, and cellular response to cisplatin-induced apoptosis and cell cycle distribution were examined by FACS analysis.
  
  
  RESULTS
  U251R cells showed 3.1-fold increase in cisplatin resistance compared to its parental U251 cells. Microarray analysis identified Let-7b and other miRNAs significantly down-regulated in U251R cells compared to U251 cells. Transfection of Let-7b mimics greatly re-sensitized U251R cells to cisplatin, while transfection of other miRNAs has no effect or slightly effect. Cyclin D1 is predicted as a target of Let-7b through bioinformatics analysis. Over-expression of Let-7b mimics suppressed cyclin D1 protein expression and inhibited cyclin D1-3'-UTR luciferase activity. Knockdown of cyclin D1 expression significantly increased cisplatin-induced G1 arrest and apoptosis.
  
  
  CONCLUSIONS
  Collectively, our results indicated that cisplatin treatment leads to Let-7b suppression, which in turn up-regulates cyclin D1 expression. Let-7b may serve as a marker of cisplatin resistance, and can enhance the therapeutic benefit of cisplatin in glioblastoma cells.
authors.affiliation: Department of Neurosurgery, Xiangya Hospital, Central South University, 410008, Changsha, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Guo
authors.forename: Kuipo
authors.initials: K
authors.lastname: Yan
authors.forename: Jiasheng
authors.initials: J
authors.lastname: Fang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Qu
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.forename: Fenghua
authors.initials: F
authors.lastname: Chen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001932:Brain Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D019938:Cyclin D1 / Q000235:genetics*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D005909:Glioblastoma / Q000235:genetics*; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D035683:MicroRNAs; C487931:mirnlet7 microRNA, human; D019938:Cyclin D1; D002945:Cisplatin